Electrolytic process



- Aug. 22, 1967 e. T. MILLER ELECTROLYTIC PROCESS Filed March 4, 1963 fzz fly- 1 United States Patent 3,337,433 ELECTROLYTIC PROCESS George T.Miller, Lewiston, N.Y., assignor to Hooker Chemical Corporation, NiagaraFalls, N.Y., a corporation of New York Filed Mar. 4, 1963, Ser. No.262,498 Claims. (Cl. 204-86) This invention is a continuation in part ofapplication SN. 45,669, now U.S. Patent 3,109,795, issued Nov. 5, 1963.

This invention relates to an electrolytic cell and more particularly toa diaphragm in an electrolytic cell.

In some electrolytic cells, a reactive material present in the cellreacts with one of the products being produced at either the anode orthe cathode of the cell to produce an end product. It has been foundthat in certain cells of this type a shut-down of the cell for cleaningof the diaphragm becomes desirable when the reactive material includedin the cell Wets or builds up on the diaphragm. Build-up of the reactivematerial on the diaphragm, if it does not cause the cell to malfunction,causes at least a decrease in the efficiency of the cell and acorresponding decrease in the yield of the desired end product. Thebuild-up of the reactive material on the diaphragm may also cause anincrease in the electrical power needed for operation of the cell, thusincreasing the cost of operating the cell and adding to the electricalload of the installation.

Build-up on the diaphragm has been found to occur in an electrolyticphosphine producing cell. In such a cell, phosphorus is the materialwhich wets the diaphragm and reacts with the electrolytic productfor-med at the cathode. Such build-up of a wetting material, phosphorus,may be prevented by means of the present invention.

It is an object of this invention to provide an improved electrolyticcell.

Another object of the invention is to prevent the wetting of a diaphragmby a reactive material contained within an electrolytic cell, therebyincreasing cell life and efficiency.

Another object is to protect a diaphragm in an electrolytic cell whichis wetted by a reactive material contained within the cell.

A further object is to inhibit wetting of a diaphragm by moltenphosphorus in an electrolytic cell producing phosphine.

The invention has particular application to uses in which the reactivematerial is phosphorus and a product of the cell is phosphine. Anotheraspect of the invention which is of importance is the structure of thecovered or sheathed diaphragm and the materials thereof.

In accordance with thisinvention, it has been found that an electrolyticcell will be of increased efliciency when it comprises anodic andcathodic electrodes, a diaphragm separating anode and cathode, anelectrolyte in contact with the electrodes and the diaphragm, from whichelectrolyte a product of electrolysis is formed at an electrode when anelectric current flows between the electrodes through the electrolyte,and a reactive material 3,337,433 Patented Aug. 22, 1967 14, cathodecompartment 16, and cathode 18. A porous or permeable diaphragm 20separates anode and cathode compartments and separates the electrolyteinto anolyte 17 and catholyte 19 sections. In the cathode compartment 16is a reactive material 24, e.g., phosphorus, in liquid state. Diaphragm20 is covered, coated, or protected in such a manner that the sidethereof facing the reactive material, where it may otherwise contactthat material, is coated with a coating, cover or sheath 22 againstwhich the reactive material then does not adhere or wet the coating,which action is evidenced by convex meniscus 21. Ports 26 and 28 permitthe addition and removal of anolyte from the anode section 12. Ports 30and 32 permit the addition and removal of catholyte from the cathodesection 16. Port 34 permits the addition and removal of the reactivematerial from cathode section 16. Suflicient reactive material 24 isadded to the cathode compartment 16 to contact the portion or edge ofcathode 18, permitting contact of the reactive material with a greatersurface of the cathode by a wetting action. Anolyte gas discharge port36 is provided in the top of the anode section to remove analyte gasfrom the electrolytic cell. Catholytic gas discharge port 38 is providedon the top of the cathode section 16 to remove catholyte gas. Gas-liquidinterfaces are indicated at 15.

Electrolyzing current to the electrodes is transmitted by anodeelectrical connector 40 and cathode electrical connector 42 joining theanode and cathode to the positive and negative poles, respectively, of asource of direct current 44.

If desired, a heating or cooling means, such as a constant temperaturehath, not shown, may be employed to maintain the cell at or near adesired temperature.

Cell vessel 10 may be constructed of a material capable of resistingcorrosion by the electrolyte and other materials employed in the cell.Typical examples of suitable materials of construction of cell vessel 10include glass, glazed ceramic, tantalum, titanium, hard rubber,polyethylene, polyurethane, rigid materials coated withphenolformaldehyde resin, and the like.

Diaphragm 20 which separates the anode section 12 from the cathodesection 16 may be semipermeable or permeable material resistant to thecell contents and capable of maintaining the anode and cathode gasesseparate. Typical examples of suitable materials for use as a diaphragminclude: porous alundum, porous porcelain,

resin impregnated wool felt, and various other separators in the cell,which material is reactive with a product of electrolysis produced at anelectrode, the diaphragm having a surface thereof facing the reactivematerial which is such that electrolyte ions may pass through it and isof a material which is not wetted by the reactive material.

Other objects and aspects of the invention will be apparent from thefollowing description, taken with the drawing illustrative of theembodiment of the invention, in which drawing FIGURE 1 is a centralvertical sectional view of apparatus of this invention along 1-1, andFIGURE 2 is a horizontal sectional view along 22. Cell vessel 10,contains anode compartment 12, anode of the types which may be normallyemployed in lead storage batteries.

Cover, coating or surface 22 is a material which does not become wettedby the reactive material. Such lack of wetting effect is indicated byformation of a convex meniscus when the surface is in contact with areactive material contained in the cell. The surface, in essence,prevents the reactive material from wetting the diaphragm. In apreferred embodiment of this invention, glass fabric is the materialwhich is non-wettable by phosphorous. Examples of other non-wettablematerials suitable for the practice of this invention are vinylidenepolymers, polypropylene, polyurethane, chlorinated polyether,acrylonitrile resins, polyethylene, fluorinated hydrocarbon resins,polyester resins, polyvinyl chloride resins, graphite,phenolformaldehyde resins, natural gum rubber and chloroprene resins. Itis preferred that the above resins be fabrics thereof, but it is to beunderstood that the resins themselves in their thermosetting orthermoplastic forms may also be utilized in the invention in accordancewith the description herein. These sheathing materials also should bepermeable, non-resistance to electrochemical flow and stable in theelectrolyte media which may be utilized.

The cover material may be applied to the diaphragm by any suitablemethod, as by spraying, fusing, adhering, wrapping about the diaphragm,mechanically fastening, depositing, and integrally forming with thediaphragm. lt is preferred, however, to form a fabric material into theshape of the diaphragm, but slightly larger and then to insert thediaphragm into the preformed sheath. Alternately, one may wrap thefabric around the diaphragm and fasten it so that it will remain inplace. The diaphragm is then placed into and connected to the cellvessel 10. It is to be understood that one or both sides of thediaphragm may be coated, usually depending on which surface or surfacesmay come into contact with the reactive material.

Solid materials having a hydrogen over-voltage, as normally measured inthe absence of the reactive material, exceeding the hydrogenover-voltage of smooth platinum may be employed as the cathode. Typicalcathodic materials include lead, amalgamated lead, cadmium, tin,aluminum, nickel, alloys of nickel, such as Mumetal (an alloy containing77.2 percent nickel, 4.8 percent copper, 1.5 percent chromium, and 14.9percent iron), Monel, copper, silver, bismuth, and alloys thereof. Forexample, lead-tin, lead-bismuth, and tin-bismuth alloys may be employed.Various shapes of cathodes may be employed, e.g., the cathode may becylindrical as illustrated, or may be of plate or other shape. Mats ofmetallic wool and porous metallic sheaths may also be employed, ifdesired. Essentially the reactive material will wet such materials andrise to cover the cathode surface thinly, promoting reaction with theproduct of electrolysis generated at the cathode surface. Suitable anodematerials include lead, platinum, lead peroxide, graphite and othermaterials of construction capable of conducting current and resistingcorrosion under the conditions of electrolysis employed.

The electrolyte may be a salt or other organic or inorganic electrolytewhich is itself nonreactive with the reactive material utilized andwhich is capable of forming a product, e.g., hydrogen gas or ion, underelectrolytic conditions employed which will react with the reactivematerial. Typical examples of suitable compounds in aqueous solutionwhich may be employed as the electrolyte include hydrochloric acid,sodium chloride, lithium chloride, potassium chloride, sodium sulfate,potassium sulfate, monosodium phosphate, disodium phosphate, aceticeacid, ammonium hydroxide, phosphoric acid, sulfuric acid and mixturesthereof. The concentration of a compound in an aqueous electrolyte mayvary from about 1 to about 95 percent, but is usually between about 5and about 80 percent, preferably between about and about 50 percent.

Improved results have been obtained When metallic ions are present inthe electrolyte in small proportions. For example, suitableconcentrations of metal ions may be between 0.01 percent and 5 percentby weight of electrolyte, however, between about 0.02 percent and 3percent by weight of electrolyte may also be utilized. Preferably thoughbetween about 0.02 percent and 0.5 percent by weight of electrolyte maybe utilized. Examples of metallic ions which may be utilized areantimony, bismuth, lead, tin, cadmium, mercury, silver, zinc, cobalt,calcium, barium, and mixtures thereof. The metal ions may be placed inthe electrolyte by employing a consumable anode of the desired metal ormetals, such as a lead anode, whereby the metal ions are formed in theelectrolyte and transferred to the area adjacent to the cathode. Saltsor other compounds of the metals such as chlorides, phosphates,acetates, and the like, also may be dissolved in the electrolyte ifdesired. In another embodiment, finely divided metal in elemental formis added to the electrolyte.

The diaphragm protected in the manner illustrated and described hereinis preferably utilized in the electrolytic production of phosphine. In acell utilized for such production, the temperature of the catholyte andanolyte should be maintained above the melting point of phosphorus(about 44 degrees centigrade), and below the boiling point of theelectrolyte. Temperatures between about 60 degress centigrade and 110degrees centigrade are satisfactory, but optimum yields of phosphine areobtained at temperatures between about 70 degrees centigrade and 100degrees centigrade. When an electric current is passed through the cell,molten phosphorus on the surface of the cathode is consumed in theformation of a catholyte gas in the cathode section. The catholyte gasis predominantly phosphine, but contains some hydrogen. The anolyte gasdepends on the over-voltages of the anions in the anolyte, withreference to the anode material. Thus, for example, the anolyte gaspredominates in oxygen if sulfuric acid or phosphoric acid is used witha platinum anode, whereas for the same anode, chlorine predominates ifhydrochloric acid is used as anolyte. Thus, the coproduction of anodicoxidation products may be carried out in the anode compartment of thecell of this invention without departing from the spirit of theinvention.

As phosphorus is consumed on the surface of the cathode to yieldphosphine, additional phosphorus wets the cathode and passes from themolten pool to the vertical cathodic surface. The current density on thecathode may be controlled so that the phosphorus is consumed at a rateat which it is replenished on the cathode surface from the molten poolof phosphorus. The cathode current density may be set by the operatorand is dependent on which density gives the best results, the celldesign and the construction of the cathode. For example, when a porouslead cathode is employed, and the height of the phosphorus layer on thecathode is about 5 /2 inches, the optimum cathodic current densityappears to be between about 6 and 12 amperes per square foot. However,other current densities consistent with the economic production ofphosphine may be employed.

The phosphine containing gas produced at the cathode has a relativelyhigh concentration of phosphine, usually more than 60 percent, and itmay be as high as percent phosphine by volume or higher. The catholytegas is substantially free from other phosphorus hydrides.

In one embodiment of the invention, a lead plate is employed as thecathode, and a graphite rod is employed as the anode with an alundumdiaphragm coated with glass fabric to keep the phosphorus from thediaphragm, separating the anode from the cathode. Under theseconditions, it has been found that the operation of the cell is markedlyimproved as is further illustrated by the examples below.

In carrying out the process of the invention, it was observed that awicking action occurred at the cathode prior to energizing the cell,that is, a thin layer of molten phosphorus formed on the outer surfaceof the vertical metallic cathode above the level of the molten pool ofphosphorus before any current was impressed upon the system.

As soon as a current is caused to flow and is maintained the wickingaction becomes more rapid. It was further observed that the rate of thewicking action was faster for some metals than others, and that thethickness of the phosphorus layer on the metal surfaces was thicker onsome metals than on others. Further, in the utilization of the inventedapparatus for phosphine production when phosphorus is the reactivematerial, it has been found that the non-wetting materials, sheathingthe diaphragm prevents the diaphragm from building up a layer ofphosphorus on its surface, which otherwise would cause a decrease in theefliciency of the cell. It is to be understood that a reactive materialwhich produces a convex meniscus at the sheathing or coating of thediaphragm will not wet the diaphragm and thereby increase the efiiciencyof an electrolytic cell containing reactive material. Suitable reactivematerials which may be utilized in the apparatus of the invention aresulfur, the alkali metals and their salts, e.g., potassium, sodiumlithium, rubidium, cesium, sodium chloride, etc., alkaline earth metals,e.g., beryllium,

calcium, strongium, barium, as Well as magnesium, germanium and lead.

The porosity or openings of the coating material may be between 0.5micron and A of an inch, as desired, to block the flow of reactivematerial through the protective coating of the diaphragm.

The following examples are presented to further illustrate theinvention, without any intent of being limited thereby. All parts are byweight and all temperatures are in degrees Centigrade, unless otherwisespecified.

Example I To an electrolytic cell containing a graphite anode and leadcathode were added 2,330 parts of 10 percent hydrogen chloride solutioncontaining 1 gram per liter of lead chloride. A porous alundum diaphragmin a glass cloth sleeve with openings about 764 Of an inch, separatedthe anode and cathode so as to form anodic and cathodic compartments.266 parts of phosphorus were added to the cathodic chamber. The cell Wasmaintained at 95 degrees centigrade. An electric potential was appliedto the electrodes to cause flow of a current of about 4.6 amperes. Afterabout 102 days of continuous operation at these conditions to producephosphine at the rate of 45 grams PH /day, various ingredients beingadded as re quired, inspection revealed no wetting of the diaphragm withphosphorus and no decrease in the operational efiiciency of the cell asindicated by the fact that no change in applied voltage was required.

Example 2 Example 1 was repeated, except for the omission of the glassfabric sleeve. The cell was operated forabout 66 days. The voltageduring this period had to be increased from 4.2 to 5.3 volts. At thetime of shut down, 70 percent of the porous diaphragm area was coatedwith phosphorus and was blocked by it.

Examples 3 to 14 These examples illustrate the various nonwettablematerials which may be utilized in place of glass cloth to sheath orcover the diaphragm of the electrolytic cell of Example 1, and therebyto increase the efliciency of the cell by preventing the deposition of areactive material on its surface to block openings therein. Elementalphosphorus under concentrated hydrochloric acid was heated to celltemperature, between about 70 and 80 degrees centigrade. The followingfabrics were then tested:

Polyester (Dacron (R)) Polyvinyl chloride (Tygon(R)) Graphite (rod andfabric) Phenoliormaldehyde resins Natural gum iubber Polymer ofchloroprene (N eoprene (R)).

NNNNMN It will be recognized by those skilled in the art that variousmodifications within the invention are possible, and will be obvious toone of skill in the art, with this specification before him. Therefore,this invention is not 70 to be limited except as defined by the appendedclaims.

What is claimed is:

1. A process for producing chemicals which comprises contacting anodicand cathodic electrodes with an contact with a material reactive with aproduct of electrolysis produced there, said reactive material beingselected from the group consisting of phosphorus, sulfur, alkali metals,alkaline earth metals, magnesium, germanium, and lead, maintaining athin layer of the reactive material on the surface of said electrode,separating the anode and cathode with a diaphragm having its side facingthe electrode which contacts the reactive material covered with amaterial covered with a material against which the reactive material isnon-Wetting, and passing an electric current between the anode and thecathode through the electrolyte to produce a compound of the reactivematerial and the product of electrolysis of the electrode in contacttherewith.

2. The process of claim 1 wherein the nonwettable material is a glassfabric.

3. The process of claim 1 wherein the cathode is lead.

4. The process of claim 1 wherein the diaphragm is alundum.

5. The process of claim 1 wherein the nonwettable material is asynthetic organic plastic.

6. The process of claim 1 wherein the diaphragm is covered with a sleeveof nonwettable material.

7. A process for producing phosphine' which comprises contacting anodicand cathodic electrodes with an electrolyte, the lower portion of thecathodic electrode being in contact with phosphorus, maintaining a thinlayer of phosphorus on the surface of said cathode electrode, separating the anode and cathode with a diaphragm having its side facing thecathode covered with a material against which phosphorus is nonwetting,and passing an electric current between the anode and the cathodethrough the electrolyte to produce phosphine.

8. A process in accordance with claim 7 wherein said electrolyte isnonreactive with molten. phosphorus, and is capable of forming hydrogenions under the electrolysis conditions employed.

9. A process in accordance with claim 7 wherein the nonwettable materialis a glass fabric.

10. A process for producing phosphine, which comprises contacting anodicand cathodic electrodes with an electrolyte, the lower portion of acathodic electrode being in contact with phosphorus which is reactivewith a product of electrolysis produced there, to produce phosphine,maintaining a thin layer of phosphorus on the surface of said electrode,separating the anode and cathode with a diaphragm having a side facingthe cathodic electrode covered with a material selected from the groupconsisting of glass fabric, vinyldene polymers, polypropylene,polyurethane, chlorinated polyether, acrylonitrile resins, polyethylene,fluorinated hydrocarbon resins, polyester resins, polyvinyl chlorideresins, graphite, phenolformaldehyde resins, natural gum rubber andchloroprene resins, against which the reactive material is nonwetting,and passing an electric current between the anode and the cathodethrough the electrolyte.

References Cited UNITED STATES PATENTS 1,094,315 4/1914 Earle et al204-251 2,688,594 9/ 1954 Oosterman 20425 1 2,944,956 7/1960 Blue et a1204-266 3,017,338 1/1962 Butler 204-252 3,109,788 11/1963 Miller 2O41013,109,795 11/1963 Gordon 204-101 OTHER REFERENCES Daniels and Alberty,Physical Chemistry, second edition, 1961, pages 598-599, Wiley & sons,Inc., New York.

JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, HOWARD S. WILLIAMS,

Examiners.

electrolyte, the lower portion of an electrode being in L. G. WISE, H.M. FLOURNOY, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,337,433 August 22 1967 George T. Miller It is certified that error appearsin the above identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 22, "analyte" should read ano'lyte Column 3, lines 45 and46, "acetice" should read acetic Column 4, line 4, degress" should readdegrees Column 5, line 1, "strongium" should read strontium Column 6,line S, cancel "covered with a material", first occurrence; line 49,"vinyldene" should read vinylidene Signed and sealed this 16th day ofSeptember 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer 4 Commissioner of Patents

1. A PROCESS FOR PRODUCING CHEMICALS WHICH COMPRISES CONTACTING ANODICAND CATHODIC ELECTRODES WITH AN ELECTROLYTE, THE LOWER PORTION OF ANELECTRODE BEING IN CONTACT WITH A MATERIAL REACTIVE WITH A PRODUCT OFELECTROLYSIS PRODUCED THERE, SAID REACTIVE MATERIAL BEING SELECTED FROMTHE GROUP CONSISTING OF PHOSPHORUS, SULFUR, ALKALI METALS, ALKALINEEARTH METALS, MAGNESIUM, GERMANIUM, AND LEAD, MAINTAINING A THIN LAYEROF THE REACTIVE MATERIAL ON THE SURFACE OF SAID ELECTRODE, SEPARATINGTHE ANODE AND CATHODE WITH A DIAPHRAGM HAVING ITS SIDE FACING THEELECTRODE WHICH CONTACTS THE REACTIVE MATERIAL COVERED WITH A MATERIALCOVERED WITH A MATERIAL AGAINST WHICH THE REACTIVE MATERIAL ISNON-WETTING, AND PASSING AN ELECTRIC CURRENT BETWEEN THE ANODE AND THECATHODE THROUGH THE ELECTROLYTE TO PRODUCE A COMPOUND OF THE REACTIVEMATERIAL AND THE PRODUCT OF ELECTROLYSIS OF THE ELECTRODE IN CONTACTTHEREWITH.